Hydraulic control system

ABSTRACT

A hydraulic control system is described in which the flow of fluid to a load is first controlled by a flow control valve in accordance with a desired variation in rate of flow and then controlled by a pressure control valve in accordance with a desired variation in load pressure. An important feature is a split land in the flow control valve by which control can be shifted quickly from flow control to pressure control.

United States Patent [191 Hayner Oct. 23, 1973 [54] HYDRAULIC CONTROL SYSTEM 2,531,907 11 1950 Daubenmeyer 92 75 3,333,416 8/1967 Budzich 91 388 [75] Inventor Paul Rayner Lexmgton Mass 3,596,561 8 1971 Keller 91 32 Assignee: Sanders Associates, Inc., Nashua, N'H l,576,l25 l/l970 Germany 92/75 [22] Filed: Mar. 13, 1972 Primary ExaminerPaul E. Maslousky Att0rneyLouis Etlinger [52] US. Cl. 9l/24,99ll//3259 991203725, [57] ABSTRACT 51 1111. C1. F15!) 15/22, FlSb 12/042 A hydrauliF comm W is described in which the 58 Field of Search 91/32, 29, 388, 33, of a 021d first, contmnd by a 9? 9l/37O 371 92/75 trol valve 1n accordance w1th a desu'ed vanatlon 1n rate of flow and then controlled by a pressure control [56] References Cited valve in accordance with a desired variation in load UNITED STATES PATENTS pressure; An 1mportant feature 15 a spllt land In the flow control valve by whlch control can be shlfted 1,183,183; 3113:: glark "99/13 2253 quickly from flow control to pressure commL p1cer 1 1,777,293 10/1930 Curtis et al. 92/75 16 Claims, 6 Drawing Figures START SIGNAL i 1 /3| ,2; ,25 28, j ,21 211121" 45111101 J I a 21% SOURCE MOTOR VALVE VALVE F I MACH.

M 2 2 i 27 I SWITCH I35 BANK TRANSFER VALVE V [37 t PROGRAM ARMING TIMER V VALVE 1 1 4 ,35 ,26 S323 FORCE ESE/$1135 SOU'RCE MOTOR VALVE PAI'ENIEDHBI 23 1925 3.766.832

/o MAX.

SHEET 1 BF 4 START SIGNAL VELOCITY FLOW DIE SIGNAL FORCE PILOT CONTROL 23 CAST SOURCE MOTOR VALVE VALVE -A I I MACH.

SWITCH I35 BANK TRANSFER VALVE PROGRAM ARMING TIMER VALVE PRESSURE PRESSURE SIGNAL FORCE CONTROL SOURCE MIOTOR VALVE z 7 so i E PRESSURE D so 3 4? l 5 4o a 20 45 I I u l 9 I I m l I l l I PAIENTEBncr 23 new SHEET 2 BF 4 MOE N.

\xa x PAIENIEDumza ms 3 766.832

sum 3 m" a FIG5 HYDRAULIC CONTROL SYSTEM FIELD OF THE INVENTION This invention relates generally to hydraulic control systems and particularly to such systems which are capable of controlling selectively either the rate of flow or the pressure of fluid furnished to a useful load.

BACKGROUND In the art of die casting, a charge of material, such as molten metal, is forced into the interstices of a die, usually by means of a hydraulic ram. The quality of the resulting casting depends, to a great extent, on the program of acceleration and velocity of the ram and the pressure exerted thereby during the operation. For a particular die and a particular material, it is often found, through a combination of theory and experience, that a particular program of acceleration, velocity and pressure produces a very good casting. Once such a program is found, it is desirable to be able to repeat it for subsequent castings of the same kind. Such programming, and repetition thereof, requires control equipment for the ram which is both flexible and precise.

A typical program requires that the acceleration and velocity of the ram be controlled closely regardless of the pressure exerted until a predetermined pressure is reached, after which the pressure is controlled closely regardless of velocity. Various kinds of equipment have been used in the past to execute such programs but difficulty has been experienced in executing the change in mode of control from velocity control to pressure control. This is because, when the charge has substantially filled the die, the pressure rises very rapidly, making it difficult to change modes at the proper pressure and quickly enough to prevent excessive rise in pressure and/or excessive loading of the equipment. This difficulty has been experienced whether the change over has been done manually or automatically.

When it is attempted to shut off flow quickly by con trolling the pressure in one or both end spaces, it is found that the usual source of pilot fluid has insufficient capacity to shift the spool fast enough and in addition it is difficult. to stop the valve in the neutral position so as to avoid dropping the pressure of the load to that of the return.

Automatic changeover in response to a predetermined pressure may present an additional problem because, during normal velocity control, the pressure may vary erratically, exhibiting transient peaks" which, although of very short duration, may be of sufficient magnitude to actuate the changeover apparatus prematurely. i

It is a general object of the present invention to pro-.

SUMMARY OF THE INVENTION Briefly stated, in a valve incorporating the present invention, that land which meters the flow to the high pressure side of the load is made in two sections, moveable with respect to each other, with their junction at the associated groove. Suitable means are provided for injecting fluid under pressure to the junction between sections, thereby separating the sections and closing the passageway quickly.

BRIEF DESCRIPTION OF THE DRAWING Fora clearer understanding of the invention, refer- DESCRIPTION OF PREFERRED EMBODIMENT Referring first to FIG. 1 there is shown in block form the die casting machinery 21 which is to be controlled by the equipment of the present invention. More particularly, it is to be controlled by a hydraulic ram 22 having a piston 23 which is mechanically connected to the machinery 11 as indicated by the dotted line. The piston. 23 is also mechanically connected to operate a switch bank 24 which comprises several switches operated as the piston 23 reaches various predetermined positions. .The ram 22 is actuated by a flow control valve 25 and also by a pressure control valve 26. The

head end of the ram is connected to both of these valves by means of a hyraulic conduit 27 while the rod end is connected to the valve 25 by means of a hydraulic conduit 28. The valve 25 is a single stage spool valve, as will be more fully explained, and is controlled by a pilot valve 29 which is preferably a two stage valve as will be more fully explained. This valve in turn is controlled by a force motor 31 to which is applied an electric signal, preferably a current, obtained from a velocity signal source 32. i i i The signal source 32 maybe a conventional arrangement of electronic components such as power supplies, variable resistors and the like capable of generating a wide variety of patterns of output signals and of repeating them at will. In a typical pattern, the output may rise at a predetermined rate to a predetermined value where it may be held for a predetermined time oruntil an externally applied signal dictates a change, such as a further increase at a different rate to a second predetermined value. Such signalsources are of conventional construction and the details thereof do not form any part of the present invention. One suitable signal source is available commercially from Sanders Associates, Inc., Nashua, N.H. and is designated a Model SC Controller.

The pressure control valve 26 is preferably a two stage valve, as will be more fully explained, and it is controlled by a force motor 33 which receives signals from a pressure signal source 34 which may be identical to the source 32.

Initially, the ram 22 is controlled by the valve 25 while the valve 26 is shut off. The valve 25 causes fluid to flow into the conduit 27 at a rate determined by the signal from the source 32. The velocity of the piston 23 is, of course, directly proportional to the rate of flow of fluid through the conduit 27 into the head end of the ram 22. When the pressure in the conduit 27 rises to a predetermined value, a transfer valve 35 shuts off the valve 25 and activates the valve 26 which controls the pressure in conduit 27 in accordance with the signal from the source 34. An arming valve 36 prevents premature operation of the transfer valve 35. A program timer 37 generates signals a predetermined time after the operation of the transfer valve 35.

Referring now to FIG. 2, there is shown a graph indicating the variation in velocity of the piston 22 and the pressure in the conduit 27 during one cycle of the operation of the die casting machinery 21. Velocity variations are indicated by solid lines while pressure variations are indicated by dashed lines. Both curves are idealized to simplify explanation and it will be understood that actually the various corners of the curves would be rounded. The ordinates represent velocity and pressure in percent of maximum while the abscissa represents time although not to any particular scale. The velocity and pressure curves shown are typical of programs which have been found to produce satisfactory castings.

Referring now to FIGS. 1 and 2 together, step one indicates the beginning of the operation at which time a start signal is applied to the velocity signal source 32. This source then applies to the force motor 31 a current which rises substantially uniformly at a predetermined rate as indicated by the portion 41 of the graph until it reaches a predetermined value after which it remains constant as indicated by the curve 42. There is, of course, a correlation between elapsed time and the distance traveled by the piston 23 and step two is initiated when the piston 23 has traveled sufficiently to close one of the switches in the switch bank 24. The resultant signal is passed to the source 32 which changes its connections so as to generate an output signal which rises at a steeper rate, as indicated by the curve 43, until it reaches its maximum value where it remains steady as indicated by the curve 44. The curves 41 to 44 represent velocity of the piston 23 which, as previously explained, is determined by the rate of flow of fluid from the valve 25 into the ram 22. During this time the pressure control valve 26 is closed and has no effect.

When the die has been substantially filled with a 7 charge of material, the pressure tends to rise very quickly and unless precautions are taken it will not only rise too quickly and reach too high a level but will produce very undesirable pressure oscillations. Accordingly, it is desired to transfer control promptly from velocity control to pressure control when the pressure has risen to a predetermined value such as that indicated by the dotted line 45. However, it has been found that a simple transfer of control when the pressure first reaches this level causes erroneous operation This is because, during the early stages of velocity control, the pressure, although in general at a comparatively low level, will exhibit occasional high level spikes as indicated by the dashed curve 46. These spikes, although of short duration, may trigger the change over apparatus unless precautions are taken. Accordingly, the arming valve 36 is provided which inhibits operation of the transfer valve during the early stages of operation. For any particular casting, it is known approximately where in the travel of the piston 23, the pressure will tend to rise and one of the switches in the switch bank 24 is adjusted to be actuated a short distance before this point is reached as indicated by step 3 in FIG. 2. Such a switch actuation operates the arming valve 36 which enables operation of the transfer valve 35 so that changeover will occur the next time the pressure rises to the level of the dotted line 45.

Step 4 occurs the first time the pressure reaches the level of the dotted line 45 subsequent to enabling of the valve 35. At this time, the flow control valve 25 is suddenly shutoff in a manner to be fully explained. Also, signals are sent to the velocity signal source 32 and the pressure signal source 34 so as to terminate control by the valve 25 and initiate the control by the valve 26. The source 34 generates a signal specifying the desired pressure and the valve 26 responds by controlling the pressure in the conduit 27 accordingly. At first, the pressure'rises at a predetermined rate as indicated by the dashed line curve 47 after which it levels off as indicated by the curve 48. Step occurs a predetermined time after step 4 and is initiated by a signal from timer 37 which operates the pressure signal source 34 to call for zero pressure. Accordingly, the pressure falls to zero as indicated by the curve 49. After step 5 the die is opened and, some time later, the timer 37 sends a signal to the velocity source 32 which generates a signal directing the piston 23 to again move forward, although at a slow rate, thereby ejecting the biscuit," or completed casting. Step 6 shows the initiation of this operation which is concluded at step 7 by the actuation of a switch within the switch bank 24. Finally, the program timer 37 generates another signal which is passed to the velocity signal source 32 directing the piston to retract as shown by step 8. After another predetermined time, the timer 37 sends another signal to the source 32 calling for zero velocity, as indicated by step 9 thus conpleting one cycle of operation.

The details of the operations of the various valves, whose function has been briefly described above, will now be described in connection with the remaining figures of the drawing.

Referring now to FIG. 3 the valve 25 comprises a valve body 51 formed to define a hollow cylinder 52 in which is inserted a spool or piston indicated generally by the reference character 53. The overall length of the spool 53 is less than that of the cylinder thereby leaving end spaces 54 and 55. The end space 54 contains a weak compression spring 56 which urges the spool 53 to the right. The end space 54 is connected by means of a conduit 57 to a source of fluid under pressure indicated schematically by the letter P, and which may have, for example, a pressure of 2,300 psi. (pounds per square inch). The end space 55 is connected by means of a conduit 58 to the pilot valve 29. A control pressure generated within the valve 29 is transmitted over the conduit 58 so as to position the spool 53.

The spool 53 includes a land 60 adjacent to the end space 54 and also includes a land denoted generally by the reference character 59 but which is comprised of two discrete sections 59a and 59b. The junction of these sections is generally perpendicular to the axis of the spool and one of the sections, in this case the section 59b, is relieved on that side, or face, adjacent to section 59a so as to define a small chamber 61 between these sections. This chamber occupies only a central portion of the land and does not extend as far as the outer circumference thereof. The land section 59a, the land 60 and the portion of the spool 53 joining them are formed to define a small passageway 62 which communicates at one end with the chamber 61 and at the other end with a groove 63 formed in the outer circumference of the land 60. The valve body 51 is formed to define a passageway 64 communicating with the groove 63 at one end and connected to an external conduit 65 on the other, which conduit in turn is connected to the transfer valve 35 for a purpose which will be explained subsequently.

The spool 53 also includes a land denoted generally by the reference character 66 but which is comprised of two discrete sections 66a and 66b. The former is rigidly and permanently connected to the land but has been shown separately because, during manufacture, it is preferred to make the sections separately and then to join them together. The portions of the faces of the sections 66a and 66b facing each other are relieved to define a chamber containing a compression spring 67 which urges these sections apart. In the position of the parts illustrated in FIG. 3, the sections 66a and 66b are separated by a small distance while the sections 59a and 59b are in engagement with each other. The spool 53 also includes a land 68 adjacent to the end space 55. This land is integral with the land section 66b.

The land 68, the land sections 66b, 66a and 59b, and those portions of the spool 53 which interconnect certain of these land sections are formed to define an axial bore 69. The portion of this bore at the right end of the spool, that is, extending from the end space 55 to a point between the land 68 and the land section 66b, is of a relatively small diameter and beginning at that point is of increased diameter for the remainder of its length. A shoulder portion 71 is defined by the transition in diameters. A rod 72 makes a sliding fit within the enlarged portion of the bore and in the position of the parts as shown in FIG. 3, the left end of this rod abuts the right face of the land section 59a while the right end of this rod abuts the shoulder portion 71. The integral land sections 5% and 66a are slideable on the rod 72 as are the land sections 6612 and 68. 0 rings 73 and 74 are provided to prevent fluid leakage. The right end of the rod 72 from a point approximately at the right face of the land section 59b and extending to the shoulder portion 61 is hollow and in communication through the bore 69, with the end space 55.

The portion of the spool 53 adjacent to the right end of the right hand section 59b is formed to define a small upstanding portion 75, which, after assembly of the apparatus, amounts to a boss on the right face of the land section 5912. This portion 75 is formed to define a small rectangular radially extending slot 76 one wall of which is the right hand face of the land section 59b. This slot extends from the outer circumference of the land 59b inward to an annular groove 77 formed in the central portion of the spool 53. The rod 72 is formed with several apertures 78 in the outer wall which provide communication between the groove-77 and the interior of the rod 72 and the bore 69. There is thus complete communication from the end space to the slot 76. This arrangement is similar to that described in U.S. Pat. No. 3,561,488 granted Feb. 9, 1971 to James Otto Byers and entitled Fluid Flow Control Valve.

The interior of the hollow cylinder 52 between the land and the land 59a is connected to the return, or reservoir, indicated schematically by the letter R. Similarly, the interior of the cylinder 52 in the region between land 68 and land section 66b is also connected to return. The portion of the cylinder between land sections 59b and 66a is connected to the aforementioned source P of fluid under pressure. The valve body 51 is formed with an annular groove 841 on its interior surface located so as to embrace the junction between the land sections 59a and 59b and of a width slightly less than the combined widths of the land sections 59a and 59b so that, in the neutral position of the valve shown, the groove 81 and the conduit27 connected thereto are completely blocked. The valve body 51 is also formed with another annular groove 82 which embraces the junction between the land section 66a and 66b and is of such a width so that, in the neutral position shown in the drawing, the groove 82 and the conduit 28 connected thereto are completely blocked.

The main portion of the explanation of this valve will be deferred until the other figures of the drawing have been described. However, it may be noted now that except for the features associated with the split lands, the valve 25 is quite similar to the valves described in the aforementioned patent. When a control pressure is applied to the conduit 58, the land 68 will be displaced to the left and, through the rod 72, will similarly displace land 59a and the land 60. The spring 67 will cause the land section 59b to remain in engagement with the section 59a. The land 59b will be displaced until the flow of fluid from the conduit 58 through the bore 69 and the slot 76 is sufficient to reduce the pressure in the end space 55 to that in the end space 54, namely, the pressure of the source P. Fluid also flows from the source P to the groove 81 and the conduit 27 and the total flow will be exactly proportional to the flow occurring in the conduit 58. All this in accordance with the previously mentioned patent. If the pressure in conduit 58 is reduced below that of the source P, then the entire valve spoolwill be displaced to the right and conduit 57 will be connected to return while conduit 28 will be connected to the pressure source.

7 Referring now to FIG. 4 the pilot valve 29 is shown in more detail. This valve comprises a force motor 31, a flappervalve stage 85 and to the right thereof a spool valve second stage. The valve 29 is similar to the valve described in U.S. Pat. No. 2,896,588 granted July 28, 1959 to Paul F. I-Iayner and Zenny Olsen, and entitled Electro-I-Iydraulic Servo Valve. The force motor section and the flapper valve section are substantially identical and the only substantial difference is in the spool. In thepresent application the spool includes lands 86, 87, 88 and 89. A source of fluid under pres sure, P which may, for example, be at a pressure of 2,800 psi, is connected to a groove which, in the neutral position of the valveshown, is completely occluded by the land 87. The return is connected to a similar groove which is completely occluded by the land 88. The space between the lands 87 and 88 is connected to the conduit 58 which, it wil be recalled, conducts the control pressure to the main flow control valve 25. The flapper valve supply is designated Pp and may, for example, be at a pressure of 2,000-psi. It will be recalled I that the source P for the main flow control valve may,

for example be at a pressure of 2,300 psi. The various pressures mentioned are, of course, only illustrative. It

is necessary, however, that the source 1P be at a pres The lands 86 and 89 are formed with small circumferential grooves and the body of the valve 29 is formed with annular grooves adjacent thereto which are connected to a sump designated R (return and drain) which may be completely opened to the atmosphere. The reason for this is to minimize the leakage of fluid from the source P to the pilot source P The valve 29 operates in substantially the same way as described in the aforementioned US. Pat. No. 2,896,588. It is sufficient for present purposes to note that a signal from the source 32 applied to the force motor 31 operates, through the flapper valve 85 and conduits to the end spaces, to displace the second stage spool by an amount substantially proportional to the magnitude of the signal. This proportionality is brought about by virtue of the in line negative feedback, as more fully explained in U.S. Pat. No. 2,896,588. Therefore, a particular signal generated by the source 32 results in a corresponding displacement of the spool of the valve 29 and in a corresponding rate of flow of fluid through the conduit 58 and a proportional rate of flow of fluid through the valve 25 to the load conduit 27.

Referring now to FIG. 5, the pressure control valve 26 is shown in more detail. The previously mentioned source of pilot pressure, P is led by means of a conduit 87 through two restrictors 88 and 89 to two nozzles 91 and 92 which act on opposite sides of aflapper 93. The differential pressure thus generated is applied to opposite ends of a valve piston or spool 94 which includes two lands 95 and 96. The previously mentioned source of fluid under pressure, P is connected to a groove 97 and, in the position of the spool 94 shown in the drawing, the land 95 has partially opened a passageway between the groove 97 and the space between the lands 95 and 96. A groove 98 is connected to the return, and, in the position of the parts shown in FIG. 5, the land 96 has partially opened a passageway between the groove 98 and the space between the lands 95 and 96. This space between the lands is connected through a groove 99 to the load conduit 27. With the position of the parts shown in FIG. 5, fluid will flow from the source P through the interior of the valve to the return R, and the load conduit 27 will be subjected to a pressure intermediate that of the source P and thereturn R.

' The load conduit 27 is also connected to an internal passageway 101 where the pressure of this conduit acts on a small piston 102 which bears against the flapper 93. The force motor 33 also acts on the flapper 93. In the absence of a signal on the force motor 33, but with some pressure in the conduit 27, the piston 102 will displace the flapper ina direction shown in FIG. as upwards, thereby substantially increasing the pressure on the upper end of the land 95 and pushing the entire spool downward thereby completely occluding the groove 97 leading to the source and also the groove 99 leading to the load conduit 27. This has the effect of simply shutting off the load conduit 27 so that the valve 26 has no effect. When a signal is applied to the force motor 33, calling for a predetermined pressure at the load conduit 27, the flapper 93 will be urged downward thereby increasing the pressure on the bottom of the land 96 and displacing the spool 94 upward to some intermediate position such as that shown in the drawing. The pressure in the conduit 27 then acts through the piston 102 against the flapper 93 in opposition to the signal applied by the force motor and an equilibrium position is soon reached with the pressure in the conduit 27 equal to that dictated by the input signal to the force motor 33.

Referring now to FIG. 6, the transfer valve 35 and the arming valve 36 are shown in more detail. The transfer valve 35 includes a valve body 105 formed to define a hollow cylinder 106 which includes two annular grooves, 107 and 108. Within the cylinder 106 is a valve spool 109 which includes an upper land 111 and a lower land 112. The upper end of the cylinder 106 opens into a chamber 113 which is connected by means of a conduit 114 to the load conduit 27 so that the pressure in this conduit bears on the upper surface of the land 111. Mounted within the chamber 113 is a switch 115 which is actuated to one position when the land 111 is in the position shown in the drawing and which is actuated to another position when the land 111 is displaced downward from the position shown. The lower end of the cylinder 106 opens into a chamber 116 which is connected by means of a conduit 117 to the arming valve 36. Within the chamber 116 is a compression spring 118 which acts between an upper spring seat 119 and a lower spring seat 121. The upper spring seat 119 bears against the lower end of the spool 109 while the lower spring seat 121 bears against a set screw 122 by means of which the pressure exerted by the spring can be adjusted. The groove 107 is connected to a conduit 123 which in turn is permanently connected, through a portion of the arming valve 36, to another conduit 124 which in turn is connected to the return R. The lower groove 108 is connected by means of a conduit 125 to the source of pressure P The portion of the cylinder 106 between the grooves 107 and 108 is connected to the conduit 65, which, it will be recalled, is connected to a portion of the flow control valve 25 for a purpose which will be fully explained. With the parts in the position shown in the drawing, the land 111 is high enough so as to open a passageway from the return R through the groove 107 to the interior of.the cylinder 106 to the conduit 65. At the same time, the land 112 completely occludes the groove 108.

It is apparent that the pressure in the chamber 113 urges the spool 109 downward while the spool is urged upwardly by the spring 118 and any pressure which may exist in the chamber 116. The spool 109 is normally held in the position shown by the arming valve 36 which in effect blocks the conduit 117 thereby creating a fluid lock which prevents the downward motion of the spool 109. The anning valve 36 is essentially a normal closed valve which is opened by the energization of a solenoid. More particularly, the arming valve 36 includes a valve body 131 formed to define a hollow cylinder 132. The upper end of the cylinder 132 opens into a chamber 133 which communicates with the conduit 123 and also with the conduit 124 which, it will be recalled, is connected to the return. The cylinder 132 is formed with a groove 134 which communicates by means of a passageway 135 with the chamber 133.

Within the cylinder 132 is a spool 136 having an upper land 137 and a lower land 138. Within the chamber 133 is a compression spring 141 which, on the top, bears against the valve body and which on the bottom bears against the spring seat 142 which in turn bears against the upper end of the land 137 so as to urge the spool 136 downward. The lower end of the spool 136, below the land 138, comprises a rod 143 which extends downward and bears against a moveable armature 14d positioned to be attracted upward by the energization of a solenoid 145 which is wound about a magnetic structure 146. The cylinder 132 in the region between the lands 137 and 138 is connected to the conduit 117.

With the parts in the positions shown, the spring M1 urges the spool 136 downward to the position shown and in this position the land 137 completely occludes the groove 134. As a result, the conduit 117 is, in effect, blocked off. However, when the solenoid 145 is energized, it attracts the armature 144 thereby raising the spool 136 and opening a passageway from the interior of the cylinder to the groove 13d and the conduit 135 thereby effectively connecting the conduit 117 to the return. It will be recalled that during the first stages of each cycle of operation, it is desired that the velocity of the piston 23 of FIG. 1 be controlled in accordance with the program illustrated in FIG. 2. At this time the flow control valve 25 is operative to dispense fluid to the ram 22 at such a rate that the desired velocity profile is followed. Referring again to FIG. 3, the spool 53 of the valve 25 is displaced to the left of the position shown in this Figure so that the pressure source P is partially connected to the conduit 27 and the return R is partially connected to the conduit 23. The chamber 61 is connected by means of the conduits 62, 641 and 65 to the transfer valve 35 (FIG. 6). At this time the valve 35 is in the position shown in FIG. 6 so that the conduit 65 is connected to the return. Therefore, the chamber 61 (FIG. 3) is at return pressure and the spring 67 holds the land section 59b in engagement with the section 59a, unopposed by any fluid pressure differential. It necessarily follows that the land sections 66a and 66b are held apart. The'valve 36 (FIG. 6) is also initially in the position shown in the drawing so that the conduit 117 is blocked. Therefore, even though the pressure in the conduit 27 rises above that shown by the dotted line (FIG. 2) nothing occurs until step three is reached. It will be recalled that, at step three, the piston 23 (FIG.

11) operates one of the switchesin the switch bank 24- erted by the spring 118. When the pressure in conduit 27 rises sufficiently to overcome this spring pressure, as it does at step 4 of FIG. 2, it displaces the spool 111 downward with the result that the land lll occludes the groove 107 thereby shutting off the return from the conduit 65. At the same time, the land 108 descends thereby opening a passageway from the pressure source P through the interior of the valve to the conduit 65.

Returning to FIG. 3, the conduit 65 is in communica-, tion with the chamber 61 and accordingly, when this conduit is connected to the sourceP the land section 59b is displaced to the right. The only opposition to this displacement is the spring 67 (which is very weak indeed compared to the fluid pressures used) and the pressure in the conduit 28 which, at this time, is connected to the return R. Therefore the section 59b is displaced slightly to the right by this pressure. The pressure source P is only a pilot pressure source and has very little flow capability, but as soon as the land 5912 separates from the land 59a the pressure of the conduit 27 and the flow capability of the pressure source P enter the chamber 61 and quickly displace the land section 59b to the right a distance sufficient to cause the land section 66a to engage the land section 66b. This distance is sufficient to completely close the groove 81 thereby shutting off the load conduit completely and preventing further flow to the ram. 22 from this source. The result is that the velocity of the piston 23 falls rapidly as shown in FIG. 2. At the same time, the switch 115 (FIG. 6) is actuated by the downward movement of the spool 109 and such actuation has three effects. First, a signal is sent to the velocity signal source 32 (FIG. 1) directing it to remove the input signal from the force motor signal 31. This has the effect of returning the valve 29 (FIG. 4) to the neutral position shown with the conduit 58 effectively blocked. Such blocking creates a fluid lock which holds the spool 53 of the valve 25 (FIG. 3) in its then attained position with the groove 81 and the conduit 27 blocked. Second, actuation of the switch 115 sends a signal to the pressure signal source 34 directing it to generate a signal to be applied to the force motor 33 (FIGS. 1 and 5) indicative of the desired pressure profile as shown by FIG. 2. It will be recalled that, before the application of the signal through the force motor 33, the flapper 93 (FIG. 5) was urged upward by the pressure in conduit 27 acting on the piston 1112 thereby increasing the pressure on the upper side of the spool 94 thereby displacing the spool downward sufficiently to close off the conduits 97 and 27 from this valve. Upon receipt by the force motor 33 of the signal calling for pressure, the flapper 93 is displaced downward against the urging of the small piston 102 with the result that the spool 941 is displaced upward sufficiently so that fluid can flow from the source P through the groove 97, the interior of the cylinder and the groove 98 to the return. The conduit 27, being connected between these two grooves, will assume some pressure intermediate between that of the source P and the return. This pressure urges the small piston 102 upward against the downward urging of the force motor 33 and'an equilibrium position is soon reached with the pressure in conduit 27 equal to that dictated by the signal applied to the force motor 33. The third effect of the operation of the switch 115 of FIG. 6 is to start operation of the program timer 37 (FIG. 1). f

The pressure control valve 26 continues to operate and causes the pressure in the conduit 27 (which, it will 7 be recalled is connected to the head end of the ram 22) to follow the dashed curves 47 and 48 of the FIG. 2. At step 5, a predetermined time after step 4, the program timer 37 (FIG. 1) sends a signal to the pressure signal source 34 which in turn removes the signal entirely from the force motor 33 (FIG. 5). At this time, the piston 102 rises pushing the flapper 93 upward thereby creating differential pressures which push the spool 94 downward. As this spool first descends, the land first blocks off the groove 97 while the land 96 further opens the groove 98 thereby removing the pressure source P from the conduit 27 and connecting the con duit 27 solely to the return R. This causes the pressure in the conduit 27 to fall rapidly as indicated by the curve 49 of the FIG. 2. Referring again to FIG. 6, the reduction in pressure in the conduit 27 and the chamber 1113 allows the spring 118 to displace the spool I09 upward to the position shown in the drawing thereby disconnecting the conduit 65 from the source P and reconnecting it to the return.

The reduction in the pressure of the conduits 27 and 65 to that of the return removes the pressure from between the land sections 59a and 59b (FIG. 3). This allows the spring 67 to displace the land sections 66a and 59b to the left, sliding along the rod 72. As soon as the slot 76 reaches the groove 81, the pressure in the end space 55 is relieved by the flow of fluid through the slot 76 into the groove 81, conduit 27 and the return. Relief of the pressure in the end space 55 allows the pressure P in the end space 54 to displace the land 63, the land section 59a, the rod 72, the land section 66b and the land 68 to the right, thereby forcing more fluid from the end space 55 through the slot 76 to the conduit 27. Soon the land section 59a engages the land section 59b and thereafter all portions of the spool 55 move to the right together until the slot 76 is again out of communication with the groove 81 and in substantially the position shown in FIG. 3. There is no further displacement because there is no path for the excape of fluid from the end space 55, and the spool comes to rest substantially in the position shown in FIG. 3.

Step 5 is completed by the generation of an additional Signal from the program timer 37 which is sent to the arming valve 36 (FIG. 6) to deenergize the solenoid 144. This additional signal is delayed with respect to the previously mentioned step 5 signal (which was sent to the pressure signal source 34) sufficiently to allow time for the spool 109 of the valve 35 to be raised by the spring to the position illustrated in the drawing, as previously explained. Accordingly, the transfer valve 35 is now in its initial condition and its operation is again inhibited by the arming valve 36.

Referring again to FIG. 2, to this time the cycle has progressed through step 5. As previously mentioned, the die is opened up and sometime later, at step 6, the program timer 37 sends a signal to the velocity signal source 32 which operates the valve in the usual manner to displace the spool 53 to the left and allow fluid from source P to flow through the conduit 27 at a slow rate. This ejects the die and when the ram has advanced sufficiently it actuates another switch at step 7 to cut off the signal from the source 32 and stop the ram. Sometime later, at step 8, the program timer 37 sends another signal to the velocity signal source 32 this time directing it to reverse the direction of the ram. This signal is passed to the force motor 31 and the pilot valve 29 whichoperates in the opposite sense to connect the conduit 58 to the return line. This reduces the pressure in the end space 55 (FIG. 3) so that the pressure P in the end space 54 shifts the spool to the right thereby connecting the pressure source P to the conduit 28 and the return to the conduit 27 so that the ram is retracted. Such retraction is unopposed and does not take very long and a short time later another signal from the program timer 37 is sent to the signal source 32 which operates through the force motor 31 and the pilot valve 29 to return the flow control valve 25 to the neutral position ready for another cycle of operation.

It is apparent from the foregoing that applicant has provided a novel and improved hydraulic system. It provides for the control of either rate of flow or of pressure in an output conduit. It provides for very rapid change in control from rate of flow to pressure. The entire system is very flexible and can be adjusted to provide innumerable different programs of rate of flow and pressure sequences.

Although a preferred embodiment of the invention has been described in considerable detail for illustrative purposes, many modifications will occur to those skilled in the art. It is therefore desired that the protection afforded by Letters Patent be limited only by the true scope of the appended claims.

What is claimed is: l. A hydraulic control system, comprising a valve including a valve body formed to define a hollow cylinder and including an enlarged diameter generally annular internal groove, a valve spool including a generally cylindrical land moveable in said cylinder,

means for controlling the position of said spool and land so as to selectively close and variably open a passageway between the interior of said cylinder and said groove, 21 source of fluid under pressure, a load, and a hydraulic path including said passageway interconnecting said source and said load characterized in that said land comprises first and second discrete sections with their adjacent faces embraced by said groove and in that said system includes means for applying fluid pressure to the space between said sections.

whereby said sections separate thereby closing said passageway.

2. A hydraulic control system in accordance with claim 1 in which said means for applying includes means for connecting said space alternatively to return or to a source of fluid under pressure.

3. A hydraulic control system in accordance with claim 1 in which said means for applying includes means responsive to the occurrence at said load of a pressure in excess of a predetermined magnitude.

4. A hydraulic control system in accordance with claim 1 in which said second section of said land is mounted for limited movement away from said first section.

5. A hydraulic control system in accordance with claim 1 which includes resilient means urging said second section into engagement with said first section.

6. A hydraulic control system including a spool having a land, and moveable within a hollow cylinder formed with an interior annular groove to open and close a passageway including said groove between a load and a source of fluid under pressure characterized in that said land is formed in two discrete sections moveable axially with respect to each other and positioned with their adjacent faces embraced by said groove and in that said system includes means for injecting fluid under pressure into the space between said sections. 7

7. A hydraulic control system including a spool having a land and moveable within a hollow cylinder formed with an interior annular groove to open and close apassageway including said groove between a load and a source of fluid under pressure characterized in that said land is formed in two discrete sections moveable axially with respect to each other and positioned with their adjacent faces embraced by said groove and in that said valve is formed to define a hydraulic path communicating with the junction of said sections and with the exterior of said valve.

8. A hydraulic control system in accordance with claim 7 in which said hydraulic path includes a passageway formed in one of said sections.

9. A hydraulic control system, comprising a valve including a valve body formed to define a hollow cylinder and including first and second enlarged diameter generally annular grooves, a valve spool including first and second generally cylindrical lands moveable in said cylinder, means for controlling the position of said spool and said lands so as to variably open first and second passageways between a first interior portion of said cylinder and said first groove and between a second interior portion of said cylinder and said second groove, a source of fluid under pressure, a load including first and second fluid connections, a reservoir, a first hydraulic path including said first passageway interconnecting said source and said first fluid connection, and a second hydraulic path including said second passageway interconnecting said reservoir and said second fluid connection; characterized in that said first and second lands comprise first and second discrete sections and third and fourth discrete sections respec tively, positioned with their adjacent faces embraced by said first and second grooves, respectively, and with said first and fourth sections remote from each other, means for joining said second and third sections so as to move as a unit, means engaging said first and fourth sections such that pressure on the remote surface of one moves both, means resiliently urging said third and fourth sections apart, and means for applying fluid pressure to the space between said first and second sections.

10. A hydraulic control system in accordance with claim 9 in which said second and third sections are mounted to be moveable axially with respect to said .first and fourth sections.

11. A hydraulic control system in accordance with claim 10 in which said sections are mounted to be relatively moveable from a first position at which said first and second sections are in engagement while said third while said third and fourth sections are in engagement.

12. A hydraulic control system in accordance with claim 10 including resilient means for urging said third and fourth sections apart and said first and second sections together.

13. A hydraulic control system in accordance with claim 9 in which said means for applying includes a passageway formed in said first section and communicating with the space between said first and second sections and with the exterior of said valve body.

14. A hydraulic control system in accordance with claim 9 in which said means for applying includes means responsive to a pressure in excess of a predetermined magnitude in said first fluid connection to said load.

15. A hydraulic control system in accordance with claim 14 which includes means for normally inhibiting operation of said means responsive and which is responsive to movement of said load beyond a predetermined position for enabling operation of said means responsive. a

16. A hydraulic control system, comprising, a first valve for controlling the flow of fluid to a load in accorand fourth sections are separated to a second position at which said first and second section are separated dance with a signal indicative of a desired velocity of movement of said load, a second. valve for controlling the flow of fluid to said load in accordance with a signal indicative of a desired fiuid pressure to be exerted against said load, and means responsive to the attainment of a predetermined pressure at said load for transferring control of fluid flow from said first valve to said second valve, characterized in that said system includes means for normally inhibiting operation of said means responsive and which is responsive to the movement of said load beyond a predetermined position for enabling operation of said means responsive. 

1. A hydraulic control system, comprising a valve including a valve body formed to define a hollow cylinder and including an enlarged diameter generally annular internal groove, a valve spool including a generally cylindrical land moveable in said cylinder, means for controlling the position of said spool and land so as to selectively close and variably open a passageway between the interior of said cylinder and said groove, a source of fluid under pressure, a load, and a hydraulic path including said passageway interconnecting said source and said load characterized in that said land comprises first and second discrete sections with their adjacent faces embraced by said groove and in that said system includes means for applying fluid pressure to the space between said sections whereby said sections separate thereby closing said passageway.
 2. A hydraulic control system in accordance with claim 1 in which said means for applying includes means for connecting said space alternatively to return or to a source of fluid under pressure.
 3. A hydraulic control system in accordance with claim 1 in which said means for applying includes means responsive to the occurrence at said load of a pressure in excess of a predetermined magnitude.
 4. A hydraulic control system in accordance with claim 1 in which said second section of said land is mounted for limited movement away from said first section.
 5. A hydraulic control system in accordance with claim 1 which includes resilient means urging said second section into engagement with said first section.
 6. A hydraulic control system including a spool having a land, and moveable within a hollow cylinder formed with an interior annular groove to open and close a passageway including said groove between a load and a source of fluid under pressure characterized in that said land is formed in two discrete sections moveable axially with respect to each other and positioned with their adjacent faces embraced by said groove and in that said system includes means for injecting fluid under pressure into the space between said sections.
 7. A hydraulic control system including a spool having a land and moveable within a hollow cylinder formed with an interior annular groove to open and close a passageway including said groove between a load and a source of fluid under pressure characterized in that said land is formed in two discrete sections moveable axially with respect to each other and positioned with their adjacent faces embraced by said groove and in that said valve is formed to define a hydraulic path communicating with the junction of said sections and with the exterior of said valve.
 8. A hydraulic control system in accordance with claim 7 in which said hydraulic path includes a passageway formed in one of said sections.
 9. A hydraulic control system, comprising a valve including a valve body formed to define a hollow cylinder and including first and second enlarged diameter generally annular grooves, a valve spool including first and second generally cylindrical lands moveable in said cylinder, means for controlling the position of said spool and said lands so as to variably open first and second passagewaYs between a first interior portion of said cylinder and said first groove and between a second interior portion of said cylinder and said second groove, a source of fluid under pressure, a load including first and second fluid connections, a reservoir, a first hydraulic path including said first passageway interconnecting said source and said first fluid connection, and a second hydraulic path including said second passageway interconnecting said reservoir and said second fluid connection; characterized in that said first and second lands comprise first and second discrete sections and third and fourth discrete sections respectively, positioned with their adjacent faces embraced by said first and second grooves, respectively, and with said first and fourth sections remote from each other, means for joining said second and third sections so as to move as a unit, means engaging said first and fourth sections such that pressure on the remote surface of one moves both, means resiliently urging said third and fourth sections apart, and means for applying fluid pressure to the space between said first and second sections.
 10. A hydraulic control system in accordance with claim 9 in which said second and third sections are mounted to be moveable axially with respect to said first and fourth sections.
 11. A hydraulic control system in accordance with claim 10 in which said sections are mounted to be relatively moveable from a first position at which said first and second sections are in engagement while said third and fourth sections are separated to a second position at which said first and second section are separated while said third and fourth sections are in engagement.
 12. A hydraulic control system in accordance with claim 10 including resilient means for urging said third and fourth sections apart and said first and second sections together.
 13. A hydraulic control system in accordance with claim 9 in which said means for applying includes a passageway formed in said first section and communicating with the space between said first and second sections and with the exterior of said valve body.
 14. A hydraulic control system in accordance with claim 9 in which said means for applying includes means responsive to a pressure in excess of a predetermined magnitude in said first fluid connection to said load.
 15. A hydraulic control system in accordance with claim 14 which includes means for normally inhibiting operation of said means responsive and which is responsive to movement of said load beyond a predetermined position for enabling operation of said means responsive.
 16. A hydraulic control system, comprising, a first valve for controlling the flow of fluid to a load in accordance with a signal indicative of a desired velocity of movement of said load, a second valve for controlling the flow of fluid to said load in accordance with a signal indicative of a desired fluid pressure to be exerted against said load, and means responsive to the attainment of a predetermined pressure at said load for transferring control of fluid flow from said first valve to said second valve, characterized in that said system includes means for normally inhibiting operation of said means responsive and which is responsive to the movement of said load beyond a predetermined position for enabling operation of said means responsive. 